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Old 09-04-2003, 12:06 PM   #1
zhangxd6
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link problems


I tried to use C to call a function writing in Fortran.first I comple the subroutine.f to obj file ,say subroutine.o .then I linked the main function writing by C using command : g++ main.c subroutine.o -lm -o file.it doesnot work .I checked the function in both obj files .I found the name of subroutine are different.I tried using gcc to link them.it works fine.So my question is :How can I link them using g++ complier since I will add functions using C++ classes.
Thanks
 
Old 09-04-2003, 04:22 PM   #2
kev82
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you need to tell the compiler that the functions exported from the fortran object file should be linked C-style not C++ style, the same problem occurs when linking a C object with c++, simply enclose the function definition in
Code:
extern "C" { /* function definition here */ }
and all should be well
 
Old 09-04-2003, 04:30 PM   #3
zhangxd6
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I got
thanks
 
Old 09-07-2003, 12:55 PM   #4
eric.r.turner
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You can use the _cplusplus macro to make it so that the same source code file can compiled with either a C or C++ compiler. When compiled with a C++ compiler, the _cplusplus macro is set, so the function is declared to use C linkage:

Code:
#ifdef _cplusplus
extern "C" {
#endif

/* function declaration here */

#ifdef _cplusplus
}
#endif
BTW, the difference between C++ and C (or Fortran) functions is the order that the function arguments are pushed onto the stack. One does them left to right, the other does them right to left. I can never remember which is which!
 
Old 09-07-2003, 01:20 PM   #5
kev82
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Quote:
BTW, the difference between C++ and C (or Fortran) functions is the order that the function arguments are pushed onto the stack. One does them left to right, the other does them right to left. I can never remember which is which!
i dont believe so, as far as i know both C and C++ push there arguments starting at the right and going left(so the first argument pops off first), pascal does it the other way round i think but im not sure.

the difference between C and C++ style linkage is name mangling. C++ compilers add the argument types and other info to the symbol name thus the function 'int p(int x)' in C would be exported as simply p, but in c++ it is exported as _Z1pi(different compilers mangle differently though). this allows functions with the same name to exist in c++

extern "C" { /* symbols */ }tells the c++ compiler to export the symbols with c linkage which is not generally a good idea because it turns off all of the features that name mangling allows. you should only extern "C" functions which are exported/imported by the executable else you are unecessarily(sp?) turning off valuable parts of C++
 
Old 09-07-2003, 03:36 PM   #6
eric.r.turner
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Do you know of any sites that have a good discussion of name mangling? Googling for one didn't seem to produce any good results.

Ah, yes. I think you are correct that the order that arguments are pushed onto the stack are the same (right to left) for both C and C++. Between the Pascal convention and the C/C++ convention there's a difference in who cleans up the stack (the function before it returns, or the caller after the function returns) right?
 
Old 09-07-2003, 03:53 PM   #7
kev82
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1) not really but have a play with c++filt and nm and see what you can figure out.

2) you are probably correct about who cleans up the stack, its been a long time since ive done any assembly or pascal, im afraid i really cant remember.
 
  


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